Modern high-speed Ethernet protocols, such as 10GBASE-T and NBASE-T, rely on adaptive filters and digital signal processing circuitry to address noise that may affect the Ethernet link. Prior to operation of the link in an “online” mode, the link undergoes autonegotiation and a full training sequence to place the link in an initial state that's capable of overcoming the noise. While operating in the “online” mode, the link may briefly go “offline” due to extraneous alien crosstalk or other noise. Fast retrain sequences may bring the link back online in a very short period of time without the need to carry out a full training sequence.
Conventional fast retraining sequences for high-speed Ethernet links generally take approximately 30 milliseconds. For many applications, such time durations for retraining functions may be undesirable.